Catalyst for ammonia oxidation and the like



UNITED STATES PATENT OFFICE CATALYST FOR AMIMONIA OXIDATION AND THE LIKEGeorge M. Hickey, Paoli, Pa., assignor to J. Bishop & 00. PlatinumWorks, Malvern, Pa., a corpora tion of Pennsylvania No Drawing.Application October 29, 1930, Serial No. 492.104

9 Claims. (01. 23-234) This invention relates to a catalyst for am-' Thecobalt increases the strength and makes monia oxidation and the like,and one of its priit possible to use an extremely fine wire. It alsomary objects is to provide a catalyst which has seems togive a smallercrystal structure present a greatly improved conversion efficiency. ingmore surface area for sprouting.

- Another object of the invention is to provide a I claim:- 5 catalystwhich will become fully activated in a 1. As a new article ofmanufacture, a catalytic very short period of time. gauze for ammoniaoxidation and the like com- I have heretofore suggested the use of acatapri ing an ll y f p n m. r m and Cobalt,

lyst comprising platinum alloyed with rhodium. annealed and acid washed.The rhodium has been used in substantial per- 2. As a new article ofmanufacture, a catalytic 1 centages by weight. gauze for ammoniaoxidation and the like com- I have discovered, however, that thepercentprising an alloy of platinum, rhodium and cobalt, age of rhodiumemployed plays an important annealed to a temperature ofapproximatelypart with respect to conversion efliciency and 2000F. and acid washed. v

5 more particularly I have found that percentage 3. As a new article ofmanufacture, a catalytic of rhodium should be less than two percent, thegauze for ammonia oxidation and the like com; best results beingobtained with 1.66% of rhodium prising an alloy of platinum, rhodium andcobalt, by weight. acid washed.

By employing this preferred percentage I have 4. The method ofmanufacturing a catalyst been enabled to obtain as high as 99.2%converwhich includes preparing an alloy of platinum, 20 sion efiiciency(total ammonia oxidized) with rhodium and cobalt, forming a catalyticgauze 97.5% conversion to nitric oxide. A platinum from said alloy, andannealing the formed gauze catalyst gives about 92% to 93% efficiency,and at a temperature in the neighborhood of 2000 F. the ordinaryplatinum rhodium alloy in use gives 5. The method of manufacturing acatalyst an efiiciency somewhat higher. While the inwhich includespreparing an alloy of platinum, 25 crease in percentage obtained byusing materially rhodium and cobalt, forming a catalytic gauze less thantwo percent of rhodium appears to be from said alloy, annealing theformed gauze at a small, nevertheless it will be understood by thosetemperature in the neighborhood of 2000 F.; and skilled in the art thatthis represents in fact a very washing the formed and annealed gauzewith substantial increase because of the close approach acid. 30 to thetheoretical. 6. The method of manufacturing a catalyst The catalysts areusually in the form of a wire which includes preparing an alloy ofplatinum, gauze through which a mixture of ammonia and rhodium andcobalt, forming a catalytic gauze oxygen containing gas is passed. fromsaid alloy, and washing the formed gauze 5 I have found by annealing thewire that I am with acid.

enabled to materially cut down the time required 7. The method ofmanufacturing a catalyst before the gauze becomes fully activated.Iprefer which includes preparing an alloy of platinum to anneal to about2000 degrees Fahrenheit for and rhodium, forming a catalytic gauze fromsaid about one-half hour. alloy, and annealing the formed gauze, to pre-4 To further increase the rate of activation of pare it for catalyticreaction, by heat treatment the gauze I subject the annealed wire to anacid at a temperature in the neighborhood of 2000 F. wash, hydrochloricacid being preferred. 8. As a new article of manufacture, a catalyticThe foregoing treatment of annealing and acid gauze for ammoniaoxidation and the like comwashing results in full activation in lessthan prising an alloy of platinum, rhodium and cobalt,

three hours as against ten to twenty-four hours the rhodium and cobalttogether constituting sub- 45 required for the catalysts now employedfor the stantially less than 2% of the alloy by weight. purpose. 9. Acatalytic gauze constructed of an alloy It is possible to replace therhodium in whole comprising platinum in major proportion, and or in partby cobalt if a maximum conversion containing small amounts of rhodiumand cobalt,

5o efliciency is not desired. The cobalt should prefthe combined contentof the rhodium and cobalt erably be used, however, in larger proportionsbeing not less than 0.25% and not greater than than the rhodium. Forexample, if the rhodium 4% of the alloy. is to be entirely replaced bycobalt, the alloy GEORGE M. HICKEY, should contain about 4% of cobalt byweight.

